I ran 47 miles of the Grand Canyon in May from Rim to Rim to Rim in one day. This shirt kept me warm at the top and cool and protected at the bottom in bright sun and 100 degrees. The material is the lightest I could find and could not have done this endurance event without it. The spandex/poly material is incredible and so comfortable to wear. I recommend this shirt and brand to everyone I coach and train in Chicago.